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Re: ratio implementation
From: |
Marius Vollmer |
Subject: |
Re: ratio implementation |
Date: |
Tue, 14 Oct 2003 15:03:41 +0200 |
User-agent: |
Gnus/5.1003 (Gnus v5.10.3) Emacs/21.3 (gnu/linux) |
Bill Schottstaedt <address@hidden> writes:
> I made the requested changes (using the Oct-9 CVS Guile):
>
> ftp://ccrma-ftp.stanford.edu/pub/Lisp/gratio-1.tar.gz
With your new files, I now get
guile> (inexact->exact 123456789123456789.0)
0
This might have to do with your clever continued fraction
approximation procedure.
Also:
guile> (define pi (* 2 (acos 0)))
guile> (- (inexact->exact pi) pi)
3.31628058347633e-10
Shouldn't we be able to do better than this? Double precision is good
to about 2e-16 and I would expect the fraction returned from
inexact->exact to be accurate within that margin. (I don't know
inexact->really why I expect this, it just seems to make sense.)
What about this approach: find the integer correspondig to the bits of
the mantissa of the double number (a bignum) and then correct for the
scaling and the exponent either by multiplying with a power of two, or
building a fraction with that power of two.
I don't have the details ready yet, but I think I'll try to come up
with code for this... (when it isn't already in GMP).
- Re: ratio implementation, Marius Vollmer, 2003/10/07
- Re: ratio implementation, Marius Vollmer, 2003/10/07
- Re: ratio implementation, Bill Schottstaedt, 2003/10/13
- Re: ratio implementation,
Marius Vollmer <=
- Re: ratio implementation, Kevin Ryde, 2003/10/14
- Re: ratio implementation, Bill Schottstaedt, 2003/10/16
- Re: ratio implementation, Marius Vollmer, 2003/10/17
- Re: ratio implementation, Bill Schottstaedt, 2003/10/17
- Re: ratio implementation, Rob Browning, 2003/10/17
- Re: ratio implementation, Kevin Ryde, 2003/10/17
- Re: ratio implementation, Bill Schottstaedt, 2003/10/15
- Re: ratio implementation, Marius Vollmer, 2003/10/17
- Re: ratio implementation, Rob Browning, 2003/10/17
- Re: ratio implementation, Marius Vollmer, 2003/10/17